This study examines the role of inflammatory factors underlying the physiological and psychological symptoms associated with obstructive sleep apnea. Inflammatory markers (C reactive protein, interleukin-6, tumor necrosing factor alpha) will be examined in blood and urine in 80 patients with obstructive sleep apnea and in 25 normal controls. The study will examine the relationship between inflammatory markers, procoagulant markers, and hallmark signs of sleep apnea such as the respiratory disturbance, intermittent oxygen desaturation, elevated sympathetic nervous system activity as well as depressive symptoms, neuropsychological impairment, and quality of life. The 80 patients with sleep apnea will then be randomized for 3 weeks of treatment to either CPAP or sub-therapeutic CPAP. Treatment effects will be studied in terms of effects on procoagulant markers and on the relationship between inflammatory factors, the respiratory disturbance, intermittent oxygen desaturation, elevated sympathetic nervous system activity as well as depressive symptoms, neuropsychological impairment, and quality of life.